Ligament tensing device with displaceable lug

ABSTRACT

A ligament tensing device ( 1 ) for activating a ligament and/or capsule system during implantation of a joint implant, comprising a base body ( 2 ) having a first lug ( 3 ) with a distal bearing surface ( 4 ) resting upon a first bone, and a second lug ( 7 ) resting upon a second bone with a proximal bearing surface ( 10 ) thereof. The second lug ( 7 ) is displaceable in an anterior-posterior and/or medial-lateral direction parallel to the first lug ( 3 ).

The invention relates to a ligament-tensioning device for non-spheroidjoints in the human or animal body.

A ligament-tensioning device for non-spheroid joints is known from WO00/78225 A1. The device described therein for tensioning ligaments ofnon-spheroid joints in the human or animal body comprises a prismatic,cylindrical or plate-shaped base member having a right claw and a leftclaw, which comprise first bearing surfaces in a plane and may bebrought to bear therewith in parallel against the joint-side surface ofa first bone adjoining a non-spheroid joint. The ligament-tensioningdevice has a right handle and a left handle, a right tensioning leverand a left tensioning lever with second bearing surfaces, which arearranged parallel to the first bearing surfaces, wherein a tensioningwidth Y may be established between the respective bearing surfaces ofthe right tensioning lever and the right claw and the same or adifferent tensioning width X may be established between the respectivebearing surfaces of the left tensioning lever and the left claw. Thesecond bearing surfaces may be brought to bear against the joint-sidesurface of a second bone adjoining the joint. Moreover, the devicecomprises a right operating lever and a left operating lever, which maybe actuated individually at the same time as the device is being heldwith one hand on each corresponding handle with the respective samehand, and a right parallel displacement device and a left paralleldisplacement device, which may each be driven by the correspondingoperating lever and are each connected with a tensioning lever in such away that, when the operating lever is moved, the tensioning widths X orY respectively may be established independently of one another. Theparallel displacement devices take the form of four-bar levermechanisms.

A disadvantage of the ligament tensioning device known from WO 00/78225A1 is in particular that the joint is in itself placed under tensionafter tensioning of the ligaments. The stresses lead to high frictionalforce between the ligament tensioning device and the bone restingthereon. This may result both in damage to the adjacent bone tissueduring the course of the operation due to the friction and in suddendisplacements of the ligament-tensioning device and/or of the bone dueto ligament tension, which are uncontrollable and therefore disturb thecourse of the operation considerably.

The object of the invention is accordingly to provide a ligamenttensioning device which makes it possible to tension thecapsule-ligament structures of a joint to be provided with a prosthesiswith a parallel spreading movement and at the same time to avoidtransverse stresses with high frictional forces.

The object is achieved by the features of claim 1.

Further advantageous developments of the invention are identified in thesubclaims.

Advantageously, the second claw is of two-part construction, wherein thepart facing the bone may be displaced relative to the part of the clawconnected to the ligament tensioning device.

It is additionally advantageous for the movable part of the claw to beguided by means of a projection in a corresponding guide in the part ofthe claw connected with the ligament tensioning device.

A locking device, which may take the form for example of a tilting orrocking arm, advantageously ensures secure locking on introduction ofthe ligament-tensioning device and simple unlocking of the movable partof the claw after spreading apart.

Of particular advantage is the independent adjustability in thecraniocaudal and anteroposterior directions. Displacement in thecraniocaudal direction may for example be effected by means of aquantifiable parallel displacement device.

It is of further advantage that any desired rotational and translationaldegrees of freedom may be achieved, in order to be able to take accountof the individual anatomical parameters of any particular (knee) joint.

The invention is explained in more detail below with reference toschematic representations from different perspectives, in which:

FIG. 1 is a schematic, perspective view of an exemplary embodiment of aligament-tensioning device according to the invention, and

FIG. 2 is a schematic plan view of the exemplary embodiment of aligament-tensioning device according to the invention illustrated inFIG. 1.

FIG. 1 is a schematic, perspective overall representation of anexemplary embodiment of a ligament-tensioning device 1 configuredaccording to the invention for a knee joint, in which displaceability ofthe claws relative to one another in the anteroposterior direction isachieved.

The ligament-tensioning device 1 comprises a base member 2, which, forreliable introduction of the spreading force into the tibia, has a firstclaw 3 with a distal bearing surface 4 relative to the knee joint gap,which bearing surface 4 rests on the tibia in the case of the kneejoint. Opposite the first claw 3, a handle 5 is accordingly attached tothe base member 2, which handle 5 allows the ligament-tensioning device1 to be held and tensioned with one hand.

Likewise in accordance with the arrangement of the first claw 3 andlocated thereabove, the ligament-tensioning device 1 comprises atensioning lever 6, on which a second claw 7 is arranged. According tothe invention, the second claw 7 is of two-part construction. A firstpart 8 is connected to the tensioning lever 6, a second part 9 isarranged proximally, and displaceably, relative to the first part 8 withregard to the knee joint gap. The second part 9 comprises a proximalbearing surface 10, which bears on the opposite portion of the joint tobe treated, i.e. the femur in the case of the knee joint. The spreadingaction is produced by actuating the handle 5 together with an operatinglever 11.

With regard to the bearing surfaces 4 and 10, a parallel displacementdevice 12 allows parallel displacement of the second claw 7 with thebearing surface 10 relative to the first claw 3 with the bearing surface4. During such displacement, the second claw 7 is in active connectionwith the tensioning lever 6. In the exemplary embodiment, the paralleldisplacement device 12 is constructed as a four-bar linkage in the formof intersecting rods and comprises four levers 13, 14, 15, 16, wherein alever 13 on the tensioning lever side and a lever 16 on the base memberside are arranged in parallel, while the levers 14 and 15 cross. Thefour levers 13, 14, 15, 16 are connected together by means of five axes17, 18, 19, 20, 21. Two of the axes 17, 18 are mounted in the parallellevers 13, 16 displaceably in grooves 22, 23 extending parallel to thebearing surfaces 4, 10.

This configuration of the parallel displacement device 12 allows thelever 13 on the tensioning lever side and the lever 16 on the basemember side to move in parallel towards one another or away from oneanother. The lengths of the levers 13, 14, 15, 16 are so selected that,in the case of any desired tensioning width X between the bearingsurface 4 on the first claw 3 and the bearing surface 10 on the secondclaw 7, which may be for example between 5 mm and 40 mm, a givenconversion ratio prevails between the tensioning force applied manuallyto the handle 5 and the operating lever 11 and the distraction forceexerted on the bones adjoining the joint.

The degree of spreading force may be read off from the force display 24comprising a scale 25 and a movable display lever 26. The display lever26 is moved by the longitudinal bending of the operating lever part 27bendable by manually applied tensioning force relative to the other,display lever 26 arranged in the manner of a fork and not acted upon bythis tensioning force. If the display lever 26 and the operating leverpart 27 are moved relative to one another by means of the tensioningforce, the display lever 26 turns around a pivot 29, whereby themanually applied tensioning force is displayed on the scale 25 by thedisplay lever 26.

In addition, a locking device, not illustrated in any more detail inFIG. 1, may be provided between the handle 5 and the operating lever 11,which locking device allows the ligament-tensioning device 1 to belocked in a given position.

As already mentioned above, the second, proximal claw 7 is of two-partconstruction. The first, distal part 8 is connected to the tensioninglever 6 or is of one-piece construction therewith. The second, proximalpart 9 is arranged on the first part 8 and may be shaped like ahorseshoe, for example, in order to take account of the shape of thefemur condyles, which bear thereon.

The proximal part 9 comprises a projection 30 which extends in theanteroposterior direction in a guide 31 formed in the lever 13. Theprojection comprises catches 32, into which a locking device 33, whichin the exemplary embodiment is configured in the manner of a tilting armor rocker, engages with an appropriately shaped extension 34. Thelocking device 33 pivots about an axis 35, which is disposed on thelever 13. A free end 36 of the locking device 33 serves in actuation ofthe locking device 33.

FIG. 2 is a schematic plan view of the exemplary embodiment illustratedin FIG. 1 of a ligament-tensioning device 1 according to the invention.Identical components are provided with matching reference numerals.

As already explained with regard to FIG. 1, the ligament-tensioningdevice 1 configured according to the invention comprises a proximal claw7 which is at least partially displaceable relative to the distal claw 3and on whose bearing surface 10 the femur condyles bear in the case ofan operation on a knee joint.

In FIG. 2, the proximal part 9 of the second, proximal claw 7 is shownwith the bearing surface 10 in the unlatched state. The catches 32visible on the projection 30 are no longer in engagement with theextension 34 of the locking device 33.

The mode of operation of the ligament-tensioning device configuredaccording to the invention is as follows:

If, during preparation for a knee joint implant, a device for tensioningthe ligaments is introduced into the knee joint gap and spread apart byan amount X, forces acting obliquely, i.e. not in a craniocaudal oranteroposterior direction, may arise between the tensioning device andthe bones bearing thereon due to superimposition of the stresses inligaments and other soft tissue. These stresses, which may in principleact in any direction, may lead on the one hand, due to resultantfrictional forces, to distortion of the quantifiable craniocaudal forceand on the other hand to disturbances in the course of the operation, iffor example the bones slip off the surface of the pretensioning deviceor stresses thereby dissipate jerkily or in an uncontrolled manner.

To prevent this, the ligament-tensioning device 1 configured accordingto the invention has a claw 7 arranged so as to be displaceable in theanteroposterior direction and movable relative to the other claw 3. Thedisplaceable claw 7 is locked during introduction and spreading apart ofthe ligament-tensioning device 1 by means of the locking device 33already described. Once the desired spreading force has been reached,the operator may release the locking device 33 by pressing on the end 36thereof preferably with the thumb, such that the extension 34 is nolonger engaged with the catches 32 of the projection 30. In this way,the proximal part 9 of the claw 7 slides in the posterior direction,pulled by the femur condyles bearing on the bearing surface 10 of theclaw 7, until the knee joint is stress-free in this direction. In thisway, no jerky stress dissipation can occur during the operation. Inaddition, the frictional force on the periosteum is reduced and thelatter is thereby protected.

A scale 37 applied to the guide 31 allows quantification ofanteroposterior displacement. This is useful, for example, for detectingthe craniocaudal tensioning reaction and thus the influence of the rearcruciate ligament and other soft tissue systems on the relativedisplacement of the femur relative to the tibia and in addition formonitoring individual steps in soft tissue release. In addition, thisquantification serves in objectifying experience gained from operationsperformed, whereby the knowledge collected therefrom may have aninfluence for the purpose of increased reproducibility in futureoperations.

It is advantageous to provide a corresponding apparatus also for theother translational and rotational degrees of freedom. For example, itis possible without difficulty to allow mediolateral movement by meansof further guidance of the second part 9 of the proximal claw 7.Rotational degrees of freedom, which allow rotation about various axes,are also feasible. Spheroid joint connections between the claws 3 and 7and the ligament-tensioning device 1 would, for example, allow tiltingof the claws 3 and 7 relative to one another and could be freelyinserted into the exemplary embodiment described. The advantages of suchextensions are, in particular, problem-free adaptation to individualanatomical parameters of any particular (knee) joint and easy spreadingapart of the device for quantifying the actual craniocaudal reactionforces.

1. A ligament-tensioning device for activating the ligament and/orcapsule apparatus during implantation of a joint implant, having a basemember comprising a first claw with a distal bearing surface, whichbears on a first bone, and a second claw, which bears with a proximalbearing surface on a second bone, wherein the second claw may bedisplaced in an anteroposterior direction and/or mediolateral directionparallel to the first claw.
 2. A ligament-tensioning device according toclaim 1, wherein the second claw comprises a distal part and a proximalpart.
 3. A ligament-tensioning device accordingly to claim 2, whereinthe distal part is displaceable relative to the proximal part.
 4. Aligament-tensioning device according to claim 3, wherein the distal partof the second claw comprises a guide.
 5. A ligament-tensioning deviceaccording to claim 4, wherein a projection formed on the proximal partof the second claw is guided in the guide.
 6. A ligament-tensioningdevice according to claim 5, wherein the guide comprises a scale.
 7. Aligament-tensioning device according to claim 5, wherein the projectioncomprises catches.
 8. A ligament-tensioning device according to claim 7,wherein a locking device is provided on the second claw.
 9. Aligament-tenionsing device according to claim 8, wherein the lockingdevice engages movably in the catches.
 10. A ligament-tensioning deviceaccording to claim 9, wherein the locking device takes the form of atilting or rocking arm pivoting about an axis.
 11. A ligament-tensioningdevice according to claim 8 wherein the proximal part of the second clawmay be released relative to the distal part of the second claw byactuation of the locking device.
 12. A ligament-tensioning deviceaccording to claim 1, wherein
 13. A ligament-tensioning device accordingto claim 12, wherein the ligament-tensioning device comprises a forcedisplay for the force applied in a craniocaudal direction by theparallel displacement device.
 14. A ligament-tensioning device accordingto claim 13, characterised in that wherein the anteroposterior and/ormediolateral displacement of the first claw and the second claw relativeto one another may be effected independently of the craniocaudaldisplacement of the first claw and the second claw relative to oneanother.
 15. A ligament-tensioning device according to claim 1, whereinthe second claw is arranged in such a way that rotation of the secondclaw relative to the first claw may be effected in a varus-valgusdirection, in an internal-external direction and in theflexion-extension direction.
 16. A ligament-tensioning device accordingto claim 15, wherein the rotations in the varus-valgus direction, in theinternal-external direction and in the flexion-extension direction maybe effected independently of one another.